1. Field of the Invention
This invention relates to change gear transmissions utilizing two or more substantially identical countershaft assemblies and more particularly relates to multiple countershaft transmissions having an improved gear structure which minimizes the occurences of simultaneous gear teeth engagements, or impacts of gear meshings, to reduce the level of gear noise generated thereby.
2. Background of the Invention
Change gear transmissions utilizing two or more substantially identical countershaft assemblies are well known in the prior art. Transmissions utilizing either simple or compound mainshafts in connection with multiple countershafts wherein the mainshaft, the mainshaft gears and/or the countershaft gears are mounted in a radially floating manner relative to the other gears are also well known in the prior art. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,255,644; 3,283,613; 3,335,616; 3,349,635; 3,378,214; 3,500,695; 3,648,546; and 4,152,949, all of which are hereby incorporated by reference.
The prior art transmissions, particularly those transmissions utilizing a floating and/or pivoted mainshaft in connection with multiple substantially identical countershafts, have proven to be highly acceptable. However, as such transmissions utilize two or more countershaft gears constantly meshed with the drive or input gear and each mainshaft gear, the number of gear tooth meshings, and the noise generated thereby, is a multiple of the meshings associated with a comparable single countershaft transmission. As, for timing and indexing purposes, it is often preferable that multiple countershaft transmission countershaft gears be provided with an even number of teeth, and prior practice has been to utilize all, or substantially all, even number teeth mainshaft gears, the meshing of mainshaft gear teeth with the gear teeth on the associated countershaft gears occurred substantially, or substantially simultaneously, whereby the noise level generated thereby tended to be additive or reinforced. With the more recent emphasis on reduced noise transmissions, especially for heavy duty vehicles, this situation was not totally satisfactory.